This is the reply from Nokia Care when we asked whether "WP8.1 Update 1 users have to downgrade to get cyan update? "
"Yes, you should downgrade first the software to WP8. See this link for more
Developer preview Users
If you are registered to Windows Phone Developer Preview Program, you might need to use the Nokia Software Recovery Tool to return your Lumia to a normal commercial software before downloading the Lumia Cyan update. More information about the tool can be found here.
Remember that Cortana is initially only available for those in the US, with more territories rolling out over the coming year.
More tips and tricks for updating your Lumia can be found on our product support pages.
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